JPH0524730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a ground fault detection method for parallel multi-line circuits.

B. Summary of the Invention In a ground fault detection method for detecting ground faults in parallel multi-circuit lines, the present invention detects ground faults from the zero-sequence current of parallel multi-circuit lines, and detects ground faults at both ends of each line when the wires are disconnected. By identifying the ground fault line through fault detection, it is possible to eliminate malfunctions caused by zero-sequence circulating current between lines, and to identify faulty lines with high sensitivity.

C. Prior Art To detect ground faults in power transmission and distribution lines, zero-phase electrical quantity detection has conventionally been used for one-line ground faults, and one single-phase relay is used for three-phase circuits. For ground fault detection in parallel multi-circuit transmission and distribution lines, as shown in Figure 3 for the case of two lines, ground fault direction relays 3 _DG1 , 3 _DG2 , 4 _DG1 , 4 _DG2
A ground fault is detected in the protection system by the zero-sequence current and zero-sequence voltage in the respective lines 1L and 2L, or the neutral point current of the power transformer _.
3 _CB2 , 4 _CB1 , 4 _CB2 are to be removed. 3 _O
C1 , 3 _OC2 , 4 _OC1 , 4 _OC2 are overcurrent relays.

D. Problem to be solved by the invention In a parallel multi-circuit distribution line, if the currents in each line are balanced, no circulating current will flow.
In actual parallel multi-circuit lines, it is difficult to completely twist the cables, and due to differences in the connection positions of the busbars in the panel, the mutual impedance of each phase conductor of each line becomes unbalanced, and the zero-sequence circulating current
I _CO flows. This zero-phase circulating current I _CO may cause the ground fault direction relays 3 _DG1 , 3 _DG2 , 4 _DG1 , and 4 _DG2 to malfunction. In particular, in non-grounded parallel multi-circuit lines, it is difficult to distinguish between zero-sequence circulating current due to unbalance and zero-sequence current due to ground fault current, which poses the problem of easily causing malfunction of the ground fault relay.

E Means and Effects for Solving the Problems In view of the above problems, the present invention provides a zero-sequence current transformer that detects a zero-sequence current from a current flowing through parallel multi-circuit lines, and a detection system for this zero-sequence current transformer. A ground fault relay detects a ground fault from electric current, and when both ends of each line of parallel multi-line circuits and disconnectors are tripped for each line, the presence or absence of a ground fault in the line is determined based on whether or not the ground fault relay operates. The detection current of the zero-phase current transformer cancels out the zero-phase circulating current between the lines, and the ground fault detection for each line by batch detection of the line current sequentially detects the broken state at both ends of the line. This is determined based on whether or not a ground fault is detected.

F. Embodiment FIG. 1 is a parallel two-line protection system diagram showing an embodiment of the present invention. The differences between this figure and Figure 3 are as follows:
Instead of installing earth fault relays at both ends of both lines 1L and 2L, a set of zero-phase current transformers 5 that are common to both lines is installed inside the protection zone inside the line breaker. One ground fault relay 6 detects a ground fault within the protected area from the detected current of the phase current transformer 5.

In such a configuration, when both lines 1L and 2L are operating in parallel, the ground fault relay 6 operates in the event of a ground fault in either line 1L or 2L, and
Although a zero-sequence circulating current I _CO exists between L, it is canceled out by the current detected by the zero-sequence current transformer 5. Therefore, highly sensitive ground fault detection is possible without considering malfunctions due to zero-phase circulating current.

Here, the ground fault detection by the ground fault relay 6 is performed on the line 1.
It is not possible to determine whether the ground fault occurred in L or 2L, and whether it is inside or outside the protected area. Therefore, after the ground fault relay 6 is activated, fault line determining means is prepared.

This failed line discriminating means is constructed based on the flowchart shown in FIG. 2 lines 1L, 2
When L is running in parallel (step S1) and the ground fault relay 6 is activated (step S2), a fault line check is started (step S3), and first the line 1L is
Noshiya disconnectors 3 _CB1 and 3 _CB2 are set to the trip state (step S4), and it is determined whether or not the ground fault relay 6 operates (step S5), and if it does not operate, it is determined that there is a ground fault in the line 1 (1L). (Step S6). When it is activated, the circuit breakers 4 _CB1 and 4 _CB2 of the line 2L are disconnected (step S7), and it is determined whether or not the ground fault relay 6 is activated (step S8). If it is not activated, the line 2 ( 2L) is determined to be a ground fault (step S9), and when it operates, it is determined to be a failure outside the protected area (step S10).

Although the embodiment shows the case of two lines, it goes without saying that the present invention can be applied to multiple lines of three or more lines.

G. Effects of the Invention As described above, according to the present invention, a ground fault is detected from the zero-sequence current of multiple lines at once, and whether or not a ground fault is detected with both ends of each line broken is determined. In order to determine the presence or absence of a ground fault, detection sensitivity can be increased by preventing malfunction of ground fault detection due to zero-phase circulating current. Furthermore, faulty line identification can be performed while power transmission and distribution using other lines continues. In addition, the equipment configuration only requires one set of zero-phase current transformer, one ground fault relay, and fault line identification means.
The device configuration is simplified compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a protection system diagram showing an embodiment of the system of the present invention, FIG. 2 is a flowchart of fault line discrimination means in the system of the invention, and FIG. 3 is a conventional protection system diagram. 1L, 2L... Line, 3 _CB1 , 4 _CB1 ... Line breaker, 3 _CO1 , 4 _CO1 ... Overcurrent relay, 5... Zero phase current transformer, 6... Earth fault relay.

Claims (1)

[Claims] 1. A zero-sequence current transformer that detects zero-sequence current from the current flowing through parallel multi-circuit lines, a ground fault relay that detects ground faults from the detected current of this zero-sequence current transformer, and both ends of each line of parallel multi-circuit lines. Ground fault detection for parallel multi-line circuits, characterized in that the ground fault detection means is provided with fault line discriminating means for determining the presence or absence of a ground fault in a line based on whether or not the ground fault relay is activated when a line disconnector is tripped for each line. method.